I live in Alaska, and just had some upgrades done to my house via a Weatherization Program. The water heater and gas furnace are in the same utility room. When they were finished weatherizing my home, they found that the water heater was backdrafting, so they installed a new direct vent water heater.

Previously, the vent from the water heater and the vent from the furnace joined into one vent that went up through the roof. The new water heater has it's own vent through the wall. So - now just the furnace vents up through the roof. They changed some of the duct work so that just the furnace connects to the main duct that goes up through the roof.

Now when the furnace runs, there is a very bad smell. The best I can explain is a burning/off gassing kind of smell. At first I thought it could be off gassing from the Nashua 324A metal tape sealing the duct connections, but I would think that would have stopped after 30+ days. Additionally, when I took the furnace cover off, I noticed some "crud" in there. Little flakes or some kind of dirt. I assume this is from when they were messing with the duct?

The smell gets really bad if I raise the temp in the house 2 or more degrees (i.e. it runs for a while). I did let the weatherization people know but they were not too concerned about it. They came back, but between having the utility room door open and only letting the furnace run for a few minutes, the smell was not very strong.

Someone came into my house yesterday and could smell it, even with the utility room door shut. When we opened the door, the smell was over powering.

Before the changes were made to the venting, there was zero smell. Does anyone have any ideas?